Intake system for an internal combustion engine

ABSTRACT

PCT No. PCT/EP97/05117 Sec. 371 Date May 26, 1999 Sec. 102(e) Date May 26, 1999 PCT Filed Sep. 18, 1997 PCT Pub. No. WO98/15727 PCT Pub. Date Apr. 16, 1998An intake system for an internal combustion engine in which the intake system includes an air inlet (10), an air filter (11), a main flow duct (12) and individual ducts (13 to 16) leading from the main flow duct to the internal combustion engine cylinders. The intake system includes at least one shunt resonator (18) which includes at least one neck (20) and a resonator volume (19), the length and/or cross section of the neck (20) being variable.

BACKGROUND OF THE INVENTION

The invention relates to an intake system for an internal combustionengine.

DE OS 42 16 255 discloses an intake tube for an internal combustionengine. This intake tube is comprised of a number of individual intaketubes which are connected at the inlet end to a manifold tube. Theintake tube is made in one piece and manufactured by the blow moldingmethod. Between two individual intake tubes a shunt resonator isprovided. This is a short tube section which produces a cancellation ofsound waves of a specific frequency. The length of the tube section isto be tuned to the sound waves and amounts to λ/4. It is also possibleto connect this shunt resonator with a clean air chamber of the airfilter housing. However, an arrangement as close as possible to thesound source is preferred. The disclosed shunt resonator is effective ata specific frequency, i.e., thus also at a specific speed of theinternal combustion engine. Thus, if undesired sound waves are to bemasked out in various speed ranges of the internal combustion engine, itwould be conceivable to arrange for a plurality of shunt resonators andtune them to the corresponding frequencies. This, however, requires aconsiderable amount of space.

SUMMARY OF THE INVENTION

It is the object of the invention to avoid the aforementioneddisadvantages and provide an intake system for an internal combustionengine which has a shunt resonator which is effective over a broadfrequency spectrum, while having a volume or requiring little space.

This object is achieved by an intake system as described hereinafter.The substantial advantage of the invention is that the factors relevantto frequency are made variable and thus it is possible to adapt theshunt resonator to the motor speed in a continuous or discontinuousmanner. This adaptation is performed, for example, with dampers whichclose certain tubes or by means for varying the cross section of tubes,such as throttles operating steplessly, for example. It is also possibleto vary the length of tubes by means of a telescoping configuration.

In accordance with one embodiment of the invention it is proposed alsoto make the resonator volume variable. This is variable, for example, bydividing a large volume into a plurality of partial volumes and openingand closing these partial volumes. The size of the shunt resonator canbe varied in a simple manner depending on the rotational speed and/ordepending on the load state of the internal combustion engine. For thispurpose, appropriate speed sensors and sensors for measuring the vacuumin the intake manifold in order to determine the load state can be used.

To increase the effect of a shunt resonator, it is proposed inaccordance with another embodiment of the invention to divide the mainflow duct into segments and especially in the low-frequency range toshut off one segment, i.e., one part of the main duct.

One embodiment of the invention envisions that a first neck, commencingfrom the main duct, extends into the cavity of the shunt resonator, anda second neck having a multiple of the cross section of the first neck,is likewise connected to the main duct and the cavity of the shuntresonator. In different frequency ranges it is possible by means ofsuitable dampers to open or close both necks or only one neck.

It is proposed in a further embodiment to provide an additional neckwith a narrow cross section but with twice the length of the first neck.This neck too can be equipped with a damper and serves to suppressparticularly low frequencies in the 50 Hz range.

In accordance with a further embodiment of the invention it is proposedto attach several adjusting dampers on a single shaft. This has theadvantage that only one or two actuators are necessary for the operationof the dampers.

These and other features of preferred embodiments of the invention willbe found not only in the claims but also in the description and thedrawings, it being possible for the individual features to be realizedindividually or together in the form of sub-combinations in embodimentsof the invention and in other fields, and may represent advantageous andindependently patentable embodiments for which protection is herebyclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in further detail hereinafter with referenceto working embodiments.

FIG. 1 shows a schematic representation of an intake system,

FIGS. 2a-e show a shunt resonator with the damper positions designed forvarious frequencies,

FIGS. 3a-e show a shunt resonator with the damper positions and coupledswivel dampers.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An air intake system according to FIG. 1 comprises an air inlet 10, asubsequent air filter 11, a main flow duct 12 and, commencing from themain flow duct, individual ducts 13, 14, 15, 16, which lead to thecylinders of an internal combustion engine 17. A shunt resonator 18 iscoupled to the main flow duct. This resonator comprises a resonantcavity 19 and a resonator neck 20. As already mentioned, shuntresonators operate reliably in the frequency range to which they aretuned. They are therefore a proven means for selectively counteractingunwanted frequency ranges. For this purpose their dimensions must complywith the Helmholtz resonator formula:

    Resonance frequency f.sub.res =sound propagation velocity/2Pl*√.sub.neck area/neck length/volume

With a volume of, for example, 1500 cm³, a neck diameter of 2 cm and aneck length l of 18 cm, a resonator frequency of 58 Hz is established.When connected to the main flow duct 12 of a 4-cylinder 4-cycle motor,the shunt resonator 18 has a canceling action on the second order of themotor frequency at n=1,750 rpm. The greater the ratio of neckcross-sectional area main stream/main duct cross-sectional area is, thebetter the effect will be. If it is desired to improve the effectivenessby enlarging the cross-sectional area of the neck, then in order tomaintain the f_(res), either the neck length or the volume or both mustbe increased. This is often impossible for structural reasons. Forimprovement it is also possible to make the main duct narrower. But thiswould lead to problems in the high power range of the motor.

The solution is offered by the segmentation of the main or main flowduct and a shunt resonator with an adapter circuit. The main air duct isnarrowed only in the rotational speed range in which the shunt resonatoris to operate. Since the need to suppress low-tone components existsonly in the low speed range, the main duct for operation in this rangecan have its cross section reduced without impairing the engine torque.For this purpose the flow area of the main or main flow duct 12 isdivided into three segments, as in the cross-section 21, two of whichsegments can be closed by dampers. Thus three parallel channels areformed, in which the lower two serve for connecting the shunt resonatorfor low-tone suppression. The damper of the upper, semicircularly-shapedchannel portion 22 closes whenever the speed drops below 3,000 rpm. Thedamper 23 of the left channel portion closes when the rotational speedenters the lowest range. Dampers can also serve to adjust the shuntresonator to a frequency required by a particular rotational speed. Witha system of branch ducts and dampers different resonance frequencies canbe established, each of which becomes effective when the respectiverotational speed is reached.

The system illustrations of FIGS. 2a-e show the design of a shuntresonator which in spite of being adapted for low-tones takes up a spaceof only 1,500 cm³. FIG. 2 shows the middle portion, a side elevation ofthe main duct 12 and shunt resonator 18, on the left side a sectiontaken along line A, and on the right side a section taken along line B.In the segmented main flow duct 12 a swivel damper 25 is provided whichcloses the channel portion 22, as well as a pivotable damper 26. Thiscloses the channel portion 23. Channel portion 24 is open, asillustrated in section A--A. A resonator neck 27 leads from channelportion 23 into the resonator cavity 19. In the position shown here,however, this neck is closed by a pivotable damper 28. A furtherresonator neck 29 is in communication with channel portion 24. Thisresonator neck has about twice the length of the resonator neck 27. Atits lower end there is a pivotable damper 30 which produces a shorteningor a lengthening of the resonator neck. In the position shown here it islikewise closed.

Outside of the segmented portion of the main duct 12 there is anadditional resonator neck 31. This one is in communication with the mainflow duct 12 through a rotatable damper 32. In the position shown here,this rotatable damper is closed. Another flap damper 33, which is on theresonator neck 31, is likewise closed. The damper position shown here issuitable for in the 40 Hz range, i.e., for the lower rotational speedrange. For this purpose only the channel portion 24 is open to supplyclean air to the internal combustion engine. At the same time, thischannel portion is connected with the resonator neck 29. In this way anextremely low tuning frequency can be achieved.

FIG. 2b shows a switching position in which the resonator frequency ofthe shunt resonator assumes a higher value, adapted to a higherrotational speed which is in the 60 Hz range. In comparison with theswitching position shown in FIG. 2a, only the pivotable damper 30 isopen. Thus the originally long neck is shortened and, as alreadymentioned, the resonator frequency is increased.

In FIG. 2c a switching position is achieved which produces an air intakenoise suppression at about 80 Hz. In addition to the open pivotabledamper 30, pivotable damper 28 as well as pivotable damper 26 are open.Thus the main duct is half open, as well as the two resonator neck parts27 and 29. These two equally long, thin tubes act as one tube with adoubled cross-sectional area.

FIG. 2d shows, in addition to the already open dampers, an openrotatable damper 25 which opens the upper cross section of the segmentedpart of the main flow duct. Furthermore, the pivotable damper 32 is openand thus opens up the resonator neck 31 or produces a connection to thecavity of the shunt resonator. In this switching position, the resonancefrequency lies at about 120 Hz.

In the switching position shown in FIG. 2e, the resonance frequency liesat about 165 Hz. This corresponds to a motor rotational speed of 5,300rpm of a 4-cylinder, 4-cycle motor. All pivotable dampers or rotatabledampers are open, i.e.,in comparison with the switching position in FIG.2d, only the swivel damper 33 is additionally open, which results in ashortening of the resonator neck 31.

This series of examples makes it clear that along the motor rotationalspeed range a plurality of suppression frequencies can be establishedwhich are adjusted to match the individual tones determined to beundesirable. In this manner successful noise suppression is assured withonly one fixed cavity. The closer one approaches with the branch ductsto the noise source, i.e., to the individual cylinder heads of theinternal combustion engine, the more successful the noise suppressionwill be. Therefore, it is to be recommended to situate the shuntresonator on the clean-air side of the filter, as shown in FIG. 1. Thusthe noise suppression will be carried out at a high energy level and thecomponents that follow will be subjected to less stress. This manifestsitself in reduced sound radiation from the walls of the affectedcomponents.

In FIG. 2, six individual adjusting devices are shown which are neededfor switching into five frequency levels.

In accordance with FIGS. 3a-e, it is possible to control theseindividual actuators with ultimately two servo motors. The reduction totwo servo motors or servo elements is achieved by using rotatablevalves, each of which serves two damper functions. Moreover, it ispossible to place two such multifunctional rotary valves on one shaftwhich can assume three switching positions. In this way it is possibleto serve four individual functions with a single servo motor. Theremaining two functions are assumed by two dampers mounted on one shaft,which together require the second servo motor. Here again, threeswitching positions are assumed.

FIGS. 3a-e show the corresponding principle. Each figure shows one ofthe five switching positions. The main flow tube or duct 12 containsthree channel portions. One channel portion 34 is open all the waythrough, in which case the main duct in the middle figure runsperpendicular to the plane of drawing.

A smaller channel portion 36 is provided with a rotatable valve 35. Alarger channel portion 37 is provided with a rotatable valve 38. The twochannel portions 35 and 37 are each in communication with a respectiveresonator neck 39 and 40. Channel portion 34 is in communication with aresonator neck of smaller cross section but greater length thanresonator neck 41. In the switching position shown here, which isdesigned for a frequency range of 40 Hz, only channel portion 34 of themain flow duct is in the open state. Channels 36 and 37 are each closedby the rotatable valves 38 and 35, respectively. The two rotatablevalves 38 and 35 are disposed on a common shaft 42. In resonator neck 41and in resonator neck 40 there is a pivotable damper 43 and 44,respectively. These two pivotable dampers are also fastened on a commonshaft 45.

In the rest of FIGS. 3b-3e, the other four switching positions areshown. The following table shows the individual positions, both of therotatable valves 35 and 38 and of the two pivotable dampers 43 and 44.Pivotable damper 44 is not fastened directly on the shaft 45, but isspring-biased against the window wall and does not move until a cam lobecontacts the damper. This takes place whenever the pivotable damper 43is already open by 80°. When the shaft 45 rotates further an additional80°, it moves the flap damper 44 to the open position.

    __________________________________________________________________________                                Pivotable                                                                          Pivotable                                    Switch                                                                            Active   Rotary                                                                             Rotary    damper                                                                             damper                                       step                                                                              freq.                                                                             Shaft 42                                                                           valve 35                                                                           valve 38                                                                           Shaft 45                                                                           44   43   Figure                                  __________________________________________________________________________    1   40  Pos. 0°                                                                     Closed                                                                             Closed                                                                             Pos. 0°                                                                     Closed                                                                             Closed                                                                             3a                                      2   58  Pos. 0°                                                                     Closed                                                                             Closed                                                                             Pos. 80°                                                                    Closed                                                                             Open 3b                                      3   82  Pos. 60°                                                                    Open Closed                                                                             Pos. 80°                                                                    Closed                                                                             Open 3c                                      4   116 Pos. 120°                                                                   Open Open Pos. 80°                                                                    Closed                                                                             Open 3d                                      5   116 Pos. 120°                                                                   Open Open Pos. 160°                                                                   Open Open 3e                                      __________________________________________________________________________

What is claimed is:
 1. An air intake system for an internal combustionengine, comprising an air inlet, an air filter, a mainstream line, aplurality of individual ducts extending from the mainstream line tocylinders of the internal combustion engine, and at least one shuntresonator,wherein each of said at least one shunt resonator comprises atleast one neck and a resonator volume, wherein said at least one neck isadjustable in at least one dimension selected from the group consistingof length and cross sectional area, and wherein said mainstream line isdivided into three channel portions with two of said three channelportions each having a flap valve for controlled closing of each of saidtwo channel portions and one of said three channel portions being incommunication with one of said at least one shunt resonator.
 2. Anintake system according to claim 1, wherein dimensions of the neck areadjusted in dependence on at least one engine operating parameterselected from the group consisting of rotational speed and load state.3. An intake system according to claim 1, wherein said neck dimension isadjusted by an adjustable damper.
 4. An intake system according to claim1, wherein said resonator volume is adjustable in volume.
 5. An intakesystem according to claim 4, wherein volume of the resonator volume isadjustable in dependence on at least one engine operating parameterselected from the group consisting of rotational speed and load state.6. an intake system according to claim 4, wherein said volume isadjusted by an adjustable damper.
 7. An intake system according to claim1, wherein said shunt resonator comprises first and second necksextending from said main duct to said resonator cavity, said second neckhaving a cross sectional area which is a multiple of that of the firstneck.
 8. An intake system according to claim 7, further comprising athird neck extending from said mainstream line to said resonator volume,said third neck having a cross sectional area corresponding to that ofthe first neck and a length twice that of the first neck.
 9. An intakesystem according to claim 1, wherein the mainstream line is providedwith two adjustable dampers and the neck are provided with at least twoadjustable dampers, the adjustable dampers of the mainstream line beingoperated with a single shaft, and the adjustable dampers of the necktubes being connected with a single shaft.